The long term goal of our research is to understand the molecular basis controlling cell differentiation in the skeleton with a particular emphasis on the osteoblast lineage. Cbfa1 is the only known transcription factor whose presence is absolutely required for osteoblast differentiation during embryogenesis. The experiments proposed in this application aim at identifying the cis-acting elements and trans-acting factors controlling Cbfa1 expression. We believe that this knowledge will lead to a better understanding of the molecular mechanisms inducing cell commitment and differentiation along the osteoblast lineage and therefore of osteogenesis. This in turn will help to design new therapeutic approaches for treatment of genetic or degenerative diseases caused by impaired osteoblast differentiation and function. The specific aims are: - To delineate the osteoblast-specific cis-acting element(s) present in the proximal 2.2-kb Cbfa1 promoter fragment. - To perform DNA-binding assays to identify the transcription factors binding to the cell-specific cis-acting elements present in the 2.2.-kb Cbfa1 promoter fragment. - To analyze the function of the 2.2-kb Cbfa1 proximal promoter and of the cis-acting elements it contains in transgenic mice. - To identify other cell-specific enhancer elements located outside the 2.2.-kb proximal Cbfa1 promoter.